Datasheet

Input/Output (I/O) Ports
MC68HC908JL3E Family Data Sheet, Rev. 4
108 Freescale Semiconductor
10.3 Port B
Port B is an 8-bit special function port that shares all eight of its port pins with the analog-to-digital
converter (ADC) module, see Chapter 9 Analog-to-Digital Converter (ADC).
10.3.1 Port B Data Register (PTB)
The port B data register contains a data latch for each of the eight port B pins.
PTB[7:0] — Port B Data Bits
These read/write bits are software programmable. Data direction of each port B pin is under the control
of the corresponding bit in data direction register B. Reset has no effect on port B data.
ADC[7:0] — ADC channels 7 to 0
ADC[7:0] are pins used for the input channels to the analog-to-digital converter module. The channel
select bits, ADCH[4:0], in the ADC status and control register define which port pin will be used as an
ADC input and overrides any control from the port I/O logic. See Chapter 9 Analog-to-Digital Converter
(ADC).
10.3.2 Data Direction Register B (DDRB)
Data direction register B determines whether each port B pin is an input or an output. Writing a one to a
DDRB bit enables the output buffer for the corresponding port B pin; a zero disables the output buffer.
DDRB[7:0] — Data Direction Register B Bits
These read/write bits control port B data direction. Reset clears DDRB[7:0], configuring all port B pins
as inputs.
1 = Corresponding port B pin configured as output
0 = Corresponding port B pin configured as input
NOTE
Avoid glitches on port B pins by writing to the port B data register before
changing data direction register B bits from 0 to 1.
Address: $0001
Bit 7654321Bit 0
Read:
PTB7 PTB6 PTB5 PTB4 PTB3 PTB2 PTB1 PTB0
Write:
Reset: Unaffected by reset
Alternative Function: ADC7 ADC6 AD4C5 ADC4 ADC3 ADC2 ADC2 ADC0
Figure 10-6. Port B Data Register (PTB)
Address: $0005
Bit 7654321Bit 0
Read:
DDRB7 DDRB6 DDRB5 DDRB4 DDRB3 DDRB2 DDRB1 DDRB0
Write:
Reset:00000000
Figure 10-7. Data Direction Register B (DDRB)